The objective of this grant is to determine whether transmembrane signaling and intracellular calcium regulation is impaired in T-lymphocyte subsets fr m Alzheimer's disease (AD) patients. Previous studies have suggested both a decreased proliferative response of cells from AD donors, and abnormalities in calcium homeostasis and intracellular calcium mobilization. Since intracellular free calcium ([Ca2+]i) acts as a second messenger in transmembrane signaling study of [Ca2+]i reveals the integrity of early ste s in receptor signaling pathways, and the capacity of cells to mobilize store calcium and open calcium channels. Since peripheral blood lymphocytes share many cell surface receptors in common with CNS cells, receptor signaling defects seen in T lymphocytes of AD patients may be highly relevant to the CNS pathology of AD. We will measure [Ca2+]i in individual cells of specific T-cell subsets usin a newly developed flow cytometric technique based on the dye indo-l and simultaneous immunofluorescence analysis. Stimulation of [Ca2+]i with signa s mediated through the T-cell receptor (anti-CD3) or E rosette receptor (anti-CD2) will bc examined. In addition, the newly described calcium signa s produced by antibody crosslinking, of other differentiation antigens will b assessed. To further explore the defects and mechanism involved in intracellular calcium regulation, we will distinguish between defects in calcium mobilization versus calcium channel activity and investigate if the defect is in pre- or postreception signalling. Preliminary data show that there are significant differences in the intracellular calcium response of CD4+ cells from 18 AD patients stimulated with anti-CD3 mAb compared to 18 age-matched controls. In this proposed research, a larger and better controlled sample will allow us to determine whether the immunological alteration found is correlated with either the severity of the disease, or the rate of progression, and whether these alterations could be used as a tool in the diagnoses of AD.